This invention relates generally to an electrostatographic printing machine, and more particularly concerns an apparatus for metering a quantity of fluid release material to a heated fuser member.
In a typical electrostatographic printing machine, a latent image is recorded on a surface and developed with charged particles. These charged particles are transferred to a sheet of support material. Thereafter, the particles are permanently affixed to the sheet of support material forming a copy of the original document. Electrostatographic printing includes both electrophotographic printing and electrographic printing. Electrophotographic printing utilizes a photoconductive member which is sensitized by charging thereof to a substantially uniform level. A light image of the original document is projected onto the charged portion of the photoconductive surface. The light image dissipates the charge in the irradiated areas recording thereon an electrostatic latent image. Electrographic printing differs from electrophotographic printing in that a photoconductive member or a light image is not required to create a latent image of the original document. Generally, both of the foregoing processes employ heat settable particles which are permanently affixed to the sheet of support material by the application of heat thereto.
The particles are permanently affixed to the sheet of support material by heating them to a point at which the constituents thereof coalesce and become tacky. This action causes some absorption of the particles into the fibers of the sheet of support material which may be amongst others, plain paper. As the particles cool and solidify, they form a firm bond on the sheet of support material. The use of heat to permanently affix powder images to a sheet of support material is well known in the art.
One approach for applying heat to the particles is by passing the sheet of support material with the powder image thereon through a pair of opposed rollers, at least one of which being heated. A system employing such a pair of rollers may utilize a heated roller having the outer surface thereof covered with polytetrafluoroethylene, commonly known as Teflon, to which a release agent, such as silicon oil is applied. Preferably, the Teflon layer is relatively thin and has a thickness of less than one micron. This arrangement prevents the particles from transferring from the sheet of support material to the heated roller and insures that they remain on the sheet of support material as heat is applied.
Alternatively, a metal roller may be heated and a low molecular polyethylene applied thereto as a release agent. However, polyethylene is generally a solid at room temperature. Hence, it must be maintained in a liquid state in order to be useful as a release agent. To prevent the premature failure of the release agent, it is required to keep all the release agent in a liquid state. If the polyethylene is not maintained in the liquid state, it will form oxides and the concentration thereof will prevent it from functioning as a release agent. The time required for the polyethylene release agent to fail is proportional to the quantity of release agent in this storage housing. Thus, if a release agent is only partially molten, a reduced quantity of release agent is maintained in the storage container and the oxide concentration will occur more rapidly.
Accordingly, it is a primary object of the present invention to improve a fusing apparatus by maintaining substantially all of the release agent in a liquid condition.